The present invention relates to stator bar rewinds on extant electrical power producing land based generators and particularly relates to processes for on-demand stator bar rewinds independent of original equipment manufacturer to upgrade the quality and reliability of the stator bars in extant generators.
Land based electrical generators typically comprise a plurality of stator bars disposed in slots in a stator core. As well known, each stator bar is generally comprised of a plurality of individual electrically conductive strands. Each stator bar has opposite end sections which are twisted and extend in a generally circumferential conical direction. Each end section is connected, for example by brazing, to another stator bar to complete an electrical circuit in at least one phase about the stator. Sections of the stator bars intermediate the end sections are generally rigid and extend linearly. The ends of the stator bars, oftentimes called end windings, may index conically clockwise or counterclockwise as the ends extend from the stator core and twist from the linear intermediate section. The end windings define unique shapes at opposite ends of each stator bar for each different type of generator.
Over time it has been found desirable to replace existing stator windings in older generators with new stator windings that have a variety of qualitative and reliability enhancements. For example, older stator windings in existing generators frequently have asphalt or asbestos insulation which is low performing and may not be as effective as when new. As a consequence, many generator operators are desirous of replacing these older stator windings with new stator windings affording upgraded technology. While the present invention is applicable to stator rewinds, e.g. end winding support and slot structures, connection rings, etc., the terminology stator bars will be used for convenience throughout this specification and claims with the broader meaning of windings being attributable as applicable.
In the past, generator stator bar replacement has often been performed by the supplier of the original generator, i.e., the original equipment manufacturer (OEM). These suppliers normally maintain data from the supplied original equipment and thus have on hand measurements of the stator bars unique to that particular type of generator. Consequently, the original equipment manufacturer can readily supply replacement, stator bars. Non-OEM suppliers, however, are disadvantaged since data concerning the shape of the stator bars, essential to their replacement in that particular type of generator, is not available to them. Should the generator owner desire stator bar replacement from a non-OEM supplier, typically the owner would provide a measurement outage (in contrast to a scheduled outage) to permit the supplier to measure the existing stator bars and reverse engineer the shape of the stator bars. Non-scheduled measurement outages, however, can be costly to the owner and add cost to the non-OEM supplying the replacement stator bars.
Also the design, tooling, and fabrication of the new stator bars requires substantial time subsequent to the stator bar measurement phase adding further cost. For example, additional and necessary checking for the accuracy of the shape of the replacement stator bars per se as well as their fit with the existing stator are required before the replacement stator bars can be installed. Oftentimes, the time between measurement and installation can extend out to six months or more. In addition to the measurement outage and the added lead time, further costs associated with non-OEM suppliers for replacing stator bars are incurred in relation to the costs associated with replacement of stator bars by an OEM supplier. Consequently there is a need to reduce lead time and costs associated with the replacement of stator bars in existing generators such that cost effective stator bar rewinds independent of original equipment manufacturers can be effected.